Abstract: A method of forming a composite structure having a skin, a plurality of webs and a plurality of flanges includes wrapping each of a plurality of first lay-ups around a corresponding one of a plurality of mandrels such that each first lay-up forms a skin section, a pair of opposed web sections, which extend from the skin section, and a pair of inwardly facing flange sections. The first lay-ups are aligned and a second lay-up is laid over their skin sections. A plurality of third lay-ups are laid over pairs of flange sections. A composite structure detained by this method is also disclosed.